The Oracle Linux operating system must not send Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirects.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-221881	OL07-00-040660	SV-221881r505922_rule		Medium

Description
ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages contain information from the system's route table, possibly revealing portions of the network topology.

STIG	Date
Oracle Linux 7 Security Technical Implementation Guide	2020-09-10

Details

Check Text ( C-23596r419715_chk )
Verify the system does not send IPv4 ICMP redirect messages. # grep 'net.ipv4.conf.all.send_redirects' /etc/sysctl.conf /etc/sysctl.d/* If "net.ipv4.conf.all.send_redirects" is not configured in the /etc/sysctl.conf file or in the /etc/sysctl.d/ directory, is commented out or does not have a value of "0", this is a finding. Check that the operating system implements the "all send_redirects" variables with the following command: # /sbin/sysctl -a \| grep 'net.ipv4.conf.all.send_redirects' net.ipv4.conf.all.send_redirects = 0 If the returned line does not have a value of "0", this is a finding.

Check Text ( C-23596r419715_chk )

Verify the system does not send IPv4 ICMP redirect messages.

# grep 'net.ipv4.conf.all.send_redirects' /etc/sysctl.conf /etc/sysctl.d/*

If "net.ipv4.conf.all.send_redirects" is not configured in the /etc/sysctl.conf file or in the /etc/sysctl.d/ directory, is commented out or does not have a value of "0", this is a finding.

Check that the operating system implements the "all send_redirects" variables with the following command:

# /sbin/sysctl -a | grep 'net.ipv4.conf.all.send_redirects'

net.ipv4.conf.all.send_redirects = 0

If the returned line does not have a value of "0", this is a finding.

Fix Text (F-23585r419716_fix)
Configure the system not to allow interfaces to perform IPv4 ICMP redirects. Set the system to the required kernel parameter by adding the following line to "/etc/sysctl.conf" or a configuration file in the /etc/sysctl.d/ directory (or modify the line to have the required value): net.ipv4.conf.all.send_redirects = 0 Issue the following command to make the changes take effect: # sysctl --system

Fix Text (F-23585r419716_fix)

Configure the system not to allow interfaces to perform IPv4 ICMP redirects.

Set the system to the required kernel parameter by adding the following line to "/etc/sysctl.conf" or a configuration file in the /etc/sysctl.d/ directory (or modify the line to have the required value):

net.ipv4.conf.all.send_redirects = 0

Issue the following command to make the changes take effect:

# sysctl --system